There are two juristic views. The first one states that pus nullifies ablution, whereas the second one states otherwise. You are encouraged to choose the one that your heart feels inclined to and that is easy to handle with your illness, keeping in mind that the latter view is backed by strong evidence.
Sheikh Muhammad Saleh Al-Munajjid, a prominent Saudi Islamic lecturer and author, states the following: Some of the scholars said that if the pus from wounds is a small amount, it does not nullify wudu’, but if it is a large amount then it does nullify wudu’. A group of jurists — including the Shafi`is and Imam Ahmad, according to one report narrated from him — state that anything that comes out from anywhere other than the front and back passages does not nullify wudu’, whether it is a small amount or a large amount.
They quoted the following as evidence for that:
1. The basic principle is that it does not break wudu’; whoever claims that something breaks wudu’ has to produce evidence.
2. The fact that pus is pure (tahir) is indicated by Shari`ah-based evidence, and whatever is indicated in this way cannot be changed except by further Shari`ah-based evidence.
Having said this, we do not go beyond that which is indicated by the Qur’an and the Prophetic Sunnah because we worship Allah according to what He legislated, not according to our whims and desires. We have no right to oblige people to perform wudu’ when it is not required, or to excuse them from performing it when it is required.